24 hours but unfortunately even after you delete the character you will not be able to use the same name again.
Clarification: You will not be able to use the same name again on that SERVER.
I create the character Box on Andromeda.
I delete the character Box.
Box is no longer available on Andromeda.
I change servers to Venus.
I can create the character Box on Venus.
I change server to Valkyrie.
I can create the character Box on Valkyrie.